1. Field of the Invent
The present invention relates to a downhole apparatus and more particularly to an apparatus for carrying and positioning seismic detector equipment within a wellbore.
2. Related Prior Art
A typical state of the art, sidewall clamping downhole geophone package of the type generally used in engineering geophysics work has several deficiencies.
Prior art shallow well devices were tested early in 1988 and used in a shallow, high frequency seismic experiment in Starke, Fla. The principal investigator concluded that these devices are not adequate for future needs in borehole geophysics research. Some of the shortcomings are as follows. The package is generally limited to clamping diameters of six inches or less. The maximum operating depth is two hundred feet below water level. Maintaining the required five psi packer pressure for clamping is difficult. Downhole azimuthal sensing is not included.
Oil field service companies make sidewall locking receivers for deep well operation. However, such receivers are very expensive, do not contain azimuth sensing, and do not provide continuous three point clamping. They are also very heavy, typically weighing one hundred pounds or more. The heavy weight cuts down on the ability of the receiver to respond to higher frequency seismic signals.
Other representative receiver configurations available for use in seismic well surveys were also tested. All are basically cylindrically shaped, heavy (one hundred fifty-five to two hundred seventy-five pounds), long (seven to twelve feet), and employ swing out arms for clamping. None contain built in azimuth sensing.
Prior art has disclosed many methods and apparatus for transporting various types of equipment down a wellbore for use at subsurface locations. The following patents are examples of different means for moving and positioning equipment downhole.
U.S. Pat. Nos. 4,702,343, "Non destructive Downhole Seismic Vibrator Source and Processes of Utilizing the Vibrator to Obtain Information About Geologic Formations" and 4,715,470, "Downhole Electromagnetic Seismic Source" (Paulsson) relate to seismic sources for use down a borehole which require a clamping device. FIG. 4 of the '470 patent illustrates a configuration consisting of a clamping plate hydraulically forced against one side of the borehole to securely position opposite side contact pads 132a, 132b tightly against the borehole wall. A similar clamping arrangement is shown in FIG. 3 of the '343 patent as pad 36 and opposite side gripping surfaces 32a, 32b. The alternative structure of both patents to Paulsson is a four point hydraulically actuated plurality of clamping feet as illustrated in FIG. 2 of the '470 patent. The '343 patent also includes seismic signal detector means on the tool so that it can also perform seismic logging operations. As a result, this device is a heavy weight device.
U.S. Pat. No. 4,648,478 "Device for Generating Sound Pulses Inside a Well, by Percussion" (Dedole et al.) and U.S. Pat. No. 4,699,240, "Device for Applying Pulsed Radial Stresses to the Wall of a Well" (Dedole) relate to seismic energy sources carried in a downhole tool that includes anchorage shoes which are hydraulically extendable to secure positioning in the borehole wall. The anchoring shoes are extended in a three point array to hold the downhole tool centered within the borehole. This structure is intended for heavy weight support.
U.S. Pat. No. 4,651,311 "Electrodeless Spark Discharge Acoustic Pulse Transducer for Borehole Operation" and "Asymmetrical Lateral-Force Seismic Source Transducer" (Owen et al.) relate to a downhole tool carrying an electric arc pulse transducer that is supported in a borehole by means of an expandable rubber boot.
U.S. Pat. No. 4,293,815 (West et al.) relates a magnetometer system for use downhole as the flux gate circuit and the supporting circuits are contained in a logging tool casing 16 of the non-clampable type.
U.S. Pat. No. 4,381,610 "Self-Contained Downhole Compass" (Kramer) discusses a self-contained compass apparatus that is freely suspended into a borehole to determine selected azimuth findings.
U.S. Pat. No. 3,370,657 "Stabilizer and Deflection Tool" (Antle) generally illustrates an apparatus which is used as a stabilizer between the lower end of a drill string and a rotary drill bit. This patent illustrates methods and apparatus used for stabilizing downhole equipment used for drilling.